Molten salt baths



Patented Jan. 11, 1949 2,458,663 MOLTEN SALT BATHS Hugh G. Webster,Detroit, Mich., assignor to J. H. Shoemaker, Detroit, Mich.

No Drawing. Application November 22, 1946, Serial No. 711,795

1 Claim. 1

This application relates to molten salt baths and more particularly to aprocess for maintaining such baths in satisfactory operating orfunctioning condition.

I have discovered that in the use of molten salt baths of the type withwhich I am familiar, namely, the non-electrolytic molten salt bathcontaining sodium hydroxide, sodium nitrate, and 4% or more of sodiumchloride, or the electrolytic bath containing sodium hydroxide, sodiumchloride, and at least one-half of one percent of sodium aluminate, thefunctioning of the bath is impaired by the formation in the bath ofobjectionable compounds. I havediscovered that such compounds are formedas reaction products of the molten salt with the surfaces of the metalsbeing cleaned in such baths and with oxygen. In the case of a moltensodium salt bath used in cleaning ferrous work pieces, the objectionablecompound is in the form'of sodium ferrite. In this application, Idisclose that sodium ferrite in such a bath may be removed simply bybubbling moisture in the form of steam into the bath, using any suitableapparatus for such purpose.

For an understanding of the operation of the moisture for this purpose,let us consider the following. The bath contains objectionable compoundsin the form of metal-alkali-oxide compounds, such as sodium ferrite.This has a formula of Na2Fe2O4. This is considered as if it wereNazOIFezOs. By adding moisture, we form by hydrolysis a mixture ofNazOzIhO and F8203. In this mixture, the FezOs is considered as havingbeen released from the M120. The Fe2O3 is the objectionable metal oxide.It precipitates in the bath and drops to the bottom to form a sludgewhich can be removed by commonly known suitable mechanical means forremoving sludge. The NazOIHzO returns to the bath in the form of NaOH,an original ingredient of the bath.

Now having described the herein disclosed method for maintaining a bathsatisfactorily, I claim the following:

A process for removing objectionable sodium ferrite from a, moltenalkali-salt bath comprising molten alkali salts, molten sodium hydroxideand said objectionable sodium ferrite comprising passing steam into saidbath to precipitate the ferrite, as a removable sludge, from the bath.

HUGH G. WEBSTER.

REFERENCES CITED The following references are of record in the file ofthis patent: I

Mellor, Inorganic and Theoretical Chemistry, vol. 13, page 906.

